Cedar-Apple Rust

The Junipers this week looked almost as if someone from outer space had decorated them for Christmas. These grotesque decorations are the spore-producing structures of a fungus, Gymnosporangium juniperi-virginianae, or cedar-apple rust. Inside is a gall, which is inconspicuous for most of the year. These orange, gelatinous horns swell during rainy periods in April and May and produce spores that get carried by the wind. The spores can infect apple trees a mile or more away. Spores are then produced in the leaves of infected apple trees, and in August get carried by the wind to infect new junipers. Both hosts are required for the pathogen to survive. The rust produces lesions on the fruit, which lowers the quality. Control depends upon interrupting the life cycle of the rust either by eradication of junipers or use of a fungicide.